Sour gas wells are completed with a packer in place to isolate the sour production from the annular space between the well casing inside diameter and the outside diameter of the production tubing. The packer prevents sour gas from entering the annulus and corroding the casing string, which is the barrier between the wellbore and any adjacent ground water or aquifer. In many instances, these sour producing zones are completed with uphole zones producing sweet gas from above the packer isolation inside the annular space.
Wells which are completed with both up-hole sweet annular production and lower packer-isolated sour production are produced conventionally until the sour producing well is depleted. At this stage, a conventional service rig is employed on the well and the tubing is removed, packer unset and removed. The lower sour zone is abandoned and the well is re-completed for production only from the up-hole sweet zone. Due to the nature of the sour gas production the tubing in the wells is often brittle; debris present on top of the lower packer and makes pulling the existing completion challenging and often prohibitively expensive.
Co-production of sweet gas through the annulus and sour gas through the tubing string can create other issues. Due to the significantly larger cross sectional area of the casing annulus compared to the tubing inside diameter, a larger flow rate is necessary in the annulus against comparable flowing surface pressures to maintain production above critical rates. Inevitably, a technical limit (critical production rate) is reached in the annulus before the tubing, at which point liquids begin to drop out of the gas flow and accumulate in the annulus. Liquid accumulation results in a static pressure on the annular producing zones which eventually causes production to cease from the annular zone.